The indications for which this type of implant is inserted and fixed between the spinous processes generally originate from deterioration of the intervertebral disk. In particular, when the posterior portion of an intervertebral disk has deteriorated, extension of the spine causes the two vertebrae that are separated by the disk to move towards each other abnormally. This generally causes the nerve roots to become trapped and causes the person who is affected by this problem to experience pain.
Intervertebral implants comprising a spacer that is inserted between the spinous processes and that includes fixing means are well known. These spacers, generally made of titanium alloy, present a notch at each of their ends, with the spinous processes being received in the notches. In addition, the spacer is held by ties, interconnecting the two opposite edges of each of the notches and tightened around part of the wall of each spinous processes.
Such implants limit the extent to which the vertebrae can move towards each other since, when the spine is in extension, the spinous processes tend to come into abutment against the bottoms of the opposite notches in which they are inserted. However, the material of which the spacer is made is hard compared with the material of an intervertebral disk which, when it is intact, limits the extent to which the vertebrae can move towards each other, so much so that the jolts which can be transmitted to the spine, e.g. while walking, are not damped between two vertebrae interconnected by a spacer. Furthermore, since the spacer does not have the same mechanical properties as the remaining portion of the intervertebral disk, the overall mechanical properties of the spine present significant discontinuities compared with an intact spine, thereby increasing deterioration of the intervertebral disk.